This invention relates to coated nickel-base alloys and, more particularly, to coated dispersion-modified, nickel-base alloys including Cr for improved high temperature oxidation resistance.
The commercial availability of dispersion-modified or dispersion-strengthened nickel-base alloys provided an additional family of materials for high temperature applications. Such alloys consist essentially of Ni or Ni and Cr with a relatively small amount of an oxide such as of Th, Y or La dispersed through the alloy for strengthening purposes. The ability of this type of alloy to retain much of its strength at relatively high temperatures made it attractive for certain applications including those in gas turbine engines. However, one problem which was experienced was the gross oxidation which occurred when it operated in the higher temperature areas of gas turbine engines.
A variety of coatings and coating methods have been described, typical of which is that shown in U.S. Pat. No. 3,290,126 --Monson describing the generation of a chromizing layer which is subsequently aluminized. However, attempts to apply the duplex chromizing aluminizing coating produced voiding of the base material as well as providing limited oxidation protection.